alkali and alkaline-earth metals

Alkali and alkaline-earth metals

Michael S. HillDOI: 10.1039/b612595f

This report summarises literature published during 2006, where the reactiv-ity, structure or properties of an element from either group 1 or group 2were central to the chemistry described.

Highlights

Highlights include the first molecular calcium hydride and calcium hydroxide,

several reports detailing the synergic reactivity of heterometallic ‘ate’ complexes

and the first example of a chiral main group metal based catalyst for asymmetric

hydroamination/cyclisation reactions of aminoalkenes.

1. Introduction

As has been the case in previous Annual Reports, this chapter reflects advances in

the coordination and organometallic chemistry of the elements of groups 1 and 2.

The survey covers literature which appeared in peer-reviewed journals during the

entirety of 2006. Although the elements of the s-block have played a role in the

burgeoning fields of hydrogen generation and storage and solid state (nano)

materials, many of these advances lie outside the remit of this summary and are

only included if there is a particular point of interest associated with the synthesis or

structure of the s-block metal-containing compound. For economy of space, many

instances where an organolithium or Grignard reagent has been employed in routine

C–C or M–C bond formation have also been excluded (a search of the term

‘Grignard’ alone, for example, delivered 400 hits on Web of Science for 2006).

Ternary metal hydrides of the alkali or alkaline-earth elements have been

reviewed.1 A fascinating historical perspective on the genesis of organoalkali metal

chemistry appeared at the start of 2006.2 Recent developments in the field of organic

heterobimetallic compounds and applications of synergic mixed alkali-metal-mag-

nesium or -zinc reagents in synthesis have been the subject of two closely related

reviews.3,4 The application of a number of alkali and alkaline earth metal com-

pounds was also central to a review which described developments in the ring-

opening polymerisation of cyclic esters.5 A summary of advances in the tailoring of

aggregation within heavier alkaline earth metal halides, alkoxides and aryloxides has

also appeared.6

2. Lithium

2.1 Group 14 donor ligands

It has been reported that nBuLi in diamine/dialkyl ether mixtures forms ensembles of

hetero- and homo-solvated dimers.7 Based upon NMR studies and DFT chemical

Department of Chemistry, Imperial College London, Exhibition Rd., South Kensington,London, UK. E-mail: [email protected]; Fax: +44(0)20 7594 5804; Tel: +44(0)207594 5709

Annu. Rep. Prog. Chem., Sect. A, 2007, 103, 39–53 | 39

This journal is �c The Royal Society of Chemistry 2007

REVIEW www.rsc.org/annrepa | Annual Reports APu

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http://dx.doi.org/10.1039/b612595f

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shift calculations of (�)-sparteine–phenyllithium complexes, it has been deduced

that PhLi forms a tetrameric ladder complex in hydrocarbon solution. In THF only

solvated PhLi dimers are observed, while (�)-sparteine is free in solution.8 Crystal

structures of adducts of (�)-sparteine and PhLi, PhOLi and PhLi/PhOLi revealed a

four-membered ring with two lithium centres, each capped by a (�)-sparteine ligand,as the central motif of all three compounds.9 The structures of three o-lithiated

phenyloxazolines have been studied in solution. All three compounds are mixtures of

monomers and dimers, but are converted to monomers with HMPA and PMDTA.10

Substitutions by organolithium compounds at unactivated 1-chloro-1-alkenes

occur via an alkylidene carbenoid chain mechanism. The sterically congested

products were formed with surprising ease even with RLi as bulky as 2,4,6-tri-

t-butylphenyllithium.11 The unusual lithium and sodium n-butylmagnesium com-

plexes, [(EDBP)Mg-m2-nBuLi(Et2O)]2 and [(EDBP)Na(Et2O)(MgnBu)]2, have been

synthesised and used as initiators for the polymerisation of methylmethacrylate. The

same study reported that reaction of (EDBPH2) with nBuLi gives [(EDBPH)Li-

(Et2O)3].12 The insertion reaction of a cyclohexyl isonitrile into the C–Li bond of

[{Ph2P(O)CH2}Li] has been reported and the crystal structure of the resulting

tetrameric complex [Ph2P(O)CHQCHN(Cy)Li]4 described.13 Treatment of the

phosphine-borane adduct [(Me3Si)2CHPMe2(BH3)] withnBuLi in THF gave the

contact ion multiple ‘ate’ complex, [(THF)3Li{(Me3Si)2CPMe2(BH3)}2Li], which

was subject to a dynamic equilibrium between the ate complex and a second, most

likely monomeric, species.14 Sulfones [RCH(R0)SO2Ph] were reacted with nBuLi to

yield [LiCR(R0)SO2Ph], which crystallise in 1D polymeric ladder-like structures with

no Li–C bonding.15 The syntheses of monolithiated and 1,3-dilithiated allylsilanes

were reported and rationalised by DFT methods.16 Several allylic lithium com-

pounds have also been prepared with different potential ligands tethered at C-2. In

all compounds Li is fully coordinated to the pendant ligand and is sited off the axis

perpendicular to the allyl plane.17

The silyloxy-bridged alkane [{(Me3Si)2CH(SiMe2)}2O] has been prepared by the

reaction of [(Me3Si)2CHLi] with ClSiMe2OSiMe2Cl, while the alkane [(Me3Si)-

(Me2(MeO)Si)CH(SiMe2CH2)}2] is accessible from the reaction between [(Me3Si)-

(Me2(MeO)Si)CHLi] and ClSiMe2CH2CH2SiMe2Cl under the same conditions.

Both compounds may be metallated with either MeLi or MeK to give the complexes

[{(Me3Si)2C(SiMe2)}2OK2(OEt2)]N[5(OEt2)], [{(Me3Si)(Me2(MeO)Si)C(SiMe2-

CH2)}2Li] [Li(DME)3][7(DME)3] and [{(Me3Si)(Me2(MeO)Si)C(SiMe2CH2)}2K2]N.

Treatment of [(Me3Si)2(Me2MeOSi)CH] with MeK gave the polymeric complex

[{(Me3Si)2(Me2MeOSi)C}K]N.18 The reaction of a diphosphaalkyne, with

MeLi/LiBr in the presence of TMEDA has given the first diphosphavinyl lithium

complex, which is stable at room temperature.19

Several new lithio terphenyls were reported during 2006. The synthesis and

characterisation of derivatives of [C6H3-2,6-(Dipp)2] (Ar0) have been described,

including [Ar0CH2OH], [Ar0CH2Br] and [Ar0CH2OC(O)H].20 The lithium salts of

[(IC6H-2,6-Ph2-3,5-iPr2], [IC6H-2,6-Mes2-3,5-

iPr2] (Mes = 2,4,6-trimethylphenyl),

[C6H-2,6-Trip2-3,5-Pr2] and [IC6H-2,6-Dipp2-3,5-iPr2] were obtained by treatment

with nBuLi.21

The reaction of a (Tsi)-substituted lithium bromosilylenoid with MesLi followed

by addition of MgBr2 gave a lithium mesitylsilylenoid as a complex with magnesium

bromide.22 Three novel nonsolvated gem-dilithiosilanes, R2SiLi2, were prepared by

reacting lithium metal with silyl mercury precursors. X-Ray structure analysis

showed for two of them an unprecedented coaggregation of two R2SiLi2 molecules

40 | Annu. Rep. Prog. Chem., Sect. A, 2007, 103, 39–53


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with two R0Li molecules.23 Crystal structures of the chiral lithiosilanes

[PhMe2SiLi(THF)(�)-sparteine] and [Ph2(NEt2)SiLi(�)-sparteine] have been de-

scribed.24 The reaction of [Ge{N(SiMe3)C(Ph)C(SiMe3)(C5H4N-2)}Cl] with PhCCH

and nBuLi afforded the lithium germanate [{(PhCC)3Ge}3GeLi(Et2O)3].25 Reduction

of 1,1-diphenylstannaindene with lithium gave the 1-phenyl-1-stannaindenyl anion.

This species was then reduced to provide a 1-stannaindenyl dianion which displayed

an upfield 7Li NMR suggestive of aromatic character.26


A series of alkali metal azides, [Li([12]crown-4)(N3)], [Na([15]crown-5)(N3)],

[Na([15]crown-5)(H2O)2]N3, [M([18]crown-6)(N3)(H2O)], (M=K, Rb, Cs) has been

reported.27 LDA-mediated dehydrobrominations of exo-2-bromonorbornane,

1-bromocyclooctene, and cis-4-bromo-t-butylcyclohexane were studied to reveal

an array of mechanisms based on mono-, di-, and tri-solvated monomers as well

as triple ions.28 Structural and mechanistic studies using 6Li and 15N NMR of the

LDA-mediated anionic Fries rearrangement have been undertaken. Substituents at

the meta position of the arene and the dialkylamino moiety of the carbamate

markedly influenced the relative rates of ortholithiation and rearrangement.29

[LiN(SiMe3)2] has been shown to be an excellent precatalyst for the room-tempera-

ture guanylation of a variety of aryl amines with carbodiimides and for the C–C

coupling reaction between terminal alkynes and carbodiimides to yield propiolami-

dines.30 In related work, nBuLi and [KN(SiMe3)2] have been shown to act as catalyst

precursors for the addition of P–H bonds to carbodiimides, offering a general and

atom-economical route to substituted phosphaguanidines.31 A dimeric proline

derived diamidobinaphthyl dilithium salt has provided the first example of a chiral

main group metal based catalyst for asymmetric hydroamination/cyclisation reac-

tions of aminoalkenes with ee’s 465%.32 The 6Li/15N coupling constants and the

coordination number at lithium of lithium amide dimers of five different chiral

amines show a clear difference between di-, tri- and tetra-coordinated lithium

atoms.33 Monolithiation of (S)-N-(a-methylbenzyl)allylamine, in the presence

HMPA, resulted in the asymmetric cisoid dimer [{(S)-a-[PhC(H)-

CH3(CH2CHQCH2)NLi �HMPA}2]. Attempted dilithiation of the chiral amine at

the N and vinylic C centres with nBuLi resulted in reduction of HMPA to give

[(Me2N)2POLi]6.34 The reaction of dippbian with one or two equivalents of nBuLi in

hexane produced [{dippbian(nBu)}Li(Et2O)] and [{dippbian(nBu)Li}nBuLi]2, respec-

tively.35 The solvent-dependent aggregate structures and mechanisms of alkylation

of lithiated imines have been studied in an effort to understand the structure and

reactivity of lithiated cyclohexanone N-cyclohexylimine.36 A series of alkali-metal

salts derived from sterically crowded triazenido ligands have been characterised. The

lithium derivative is dimeric whereas the potassium and caesium salts crystallise as

monomers in which the cations interact with flanking arene rings of the diaryltria-

zenides.37 Reactions of 1,3,5-triazapentadienes [N{(C3F7)C(Ar)N}2]H (Ar = Mes,

Dipp) with nBuLi afforded the corresponding lithium 1,3,5-triazapentadienyl com-

plexes.38 The dilithium salt of phenylhydrazine, forms a tetrameric cage while the

aggregation of two [B(NNPh)3]6� hexaanions, two [NHNPh]2� dianions and 16 Li+

cations results in a 32-membered cage.39

The lithium (imido)diphosphineimide [Li(Et2O){DippNPhPP(nBu)PhNDipp}] re-

acts with elemental sulfur to afford the lithium (imido)diphosphineimine sulfide,

[Li(Et2O){DippNPhP(S)P(nBu)PhNDipp}].40 The reaction of bis(cyclohexyl)carbo-



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diimide with (tBuPLi2) gave [Li4(THF)2{(tBuP)([(CyN]2C)2}2], while the analogous

reaction with bis(trimethylsilyl)carbodiimide resulted in silyl transfer to give the

lithium salts [(tBuP)(SiMe3)Li] and [Li(THF)(Me3SiNCQN)]n.41 Carbodiimides

(RN)2C have been reductively coupled with Li powder into [{Li(py)2}2(m-C2N4R4)] (R = p-tolyl) and [{Li(THF)}2(m-C2N4R4)] (R = Cy).42 Lithium amidi-

nate complexes, [Li(THF)2{(tript)C(NR)2}] have been described and shown to exist

solely as their Zsyn isomeric forms due to the steric effect of the triptycenyl moiety.43

The cluster compound Li9O2(hpp)7 (hpp = bicyclic guanidinate, 1,3,4,6,7,8-hexa-

hydropyrimido[1,2-a]pyrimidinate), has been computationally investigated. This

system is best represented as an O2� dianion embedded in a Li cluster.44 The lithium

bis–amidinate complex, [1,4-{Li(THF)2(iPrN)2C}2){2,3,5,6-C(p-C6H4

tBu)4}], has

also been prepared.44 A series of linked lithium bis(amidinate)s have been synthe-

sised by treating silyl-bridged diamines with two equivalents of nBuLi and PhCN in

sequence,45 while a series of rac t-DACH-linked lithium bis(amidinate)s have been

investigated.46 The pyrazolato complexes [(Me2pz)(THF)Li], [tBu2pzLi],

[(tBu2pzH)(tBu2pz)Li]2, were synthesised by metalation reactions between R2pzH

(R = Me, tBu) and alkyllithium.47 The lithium salts of five new tbutyl-tris(3-

hydrocarbylpyrazol-1-yl)borate ligands [tBuTp(R)]� (R = H, Me, iPr, tBu, Ph)

have been synthesised and characterised.48 Multinuclear NMR spectroscopy and

X-ray diffraction techniques have been used to identify diastereomeric mixtures of

rac- and meso-di(phosphaguanidine) compounds including their dilithio deriva-

tives.49,50 Metalation of one aryl group of Ph3PQNR (R = Me, iPr) afforded access

to the corresponding lithium salts, which in turn react with R2PCl (R = Ph, iPr) to

yield a new class of bidentate ligand featuring one iminophosphorane and one

phosphino group.51

Interest in the application and nature of lithium-containing bimetallic amides has

continued. One possible structure of a highly chemoselective zincate base for

directed ortho-metalation of alkyl benzoates and dialkyl benzamides

[(THF)Li(mtmp)(m-tBu)Zn(tBu)] has been identified crystallographically,52 and, in

work that importantly highlights the merit of approaching the heavier and lighter

s-block element reactivity as potentially divergent, distinct reaction pathways of

analogous sodium and lithium zincates toward N,N-diisopropylbenzamide have

been identified.53 [tBu2Zn(TMP)Li] has been investigated using DFT calculations,

X-ray and NMR methods. The computational results indicated that deprotonation

involving the TMP ligand on the zincate is kinetically more favorable than that

involving the alkyl.54 Introducing TMEDA to [LiZn(NR2)Me2] led to a discrete ion-

contacted zincate with TMEDA bound to lithium in the case of NR2 = TMP but to

a novel ‘‘inverse zincate’’ with TMEDA bound to zinc in the case of NR2 = SiMe3.55

The bulky lithium silylamide [(2,6-Et2C6H3NLi)(2,6-Et2C6H3NH)SiPh2] has been

prepared and characterised as a dimer.56 An attempt to prepare the bulky amine

[(ad)(Dipp)NH] (ad = adamantyl) instead resulted in a new primary amine, [4-ad-

2,6-(Dipp)NH2] which could be converted into a dimeric lithium salt.57 Reaction of

the terphenyl derivative [BrMgArMes2] (ArMes2 = C6H3-2,6-Mes2) with p-tolue-

nesulfonyl azide afforded the azide [N3ArMes2]. Treatment of this with LiAlH4 gave

the amine H2NArMes2 in high yield. Metallation afforded the corresponding lithium

derivative [Li(H)NArMes2]. The related amine [HN(Me)ArMes2] was also synthe-

sised by reaction of the bulky amine with methyl iodide. Reaction of this compound

with nBuLi provided the dimeric lithium derivative [LiN(Me)ArMes2]2.58

The secondary phosphines, [Ar(C6H4-2-CH2NMe2)PH] (Ar = Mes, trip) have

been metallated. [Li(12-crown-4)2][(Mes)(C6H4-2-CH2NMe2)P] exists as a separated



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ion pair complex. The lithium complexes undergo metathesis reactions with either

NaOtBu or KOtBu to give the heavier alkali metal phosphides.59 Reactions of

[Sn(NMe2)2] and (tBuPHM) (M = Li, Na, K) resulted in the formation of

heterometallic phosphinidene cages.60 The synthesis of the lithium oligophosphane-

diides, [Li2(PnPhn)(TMEDA)x] (n = 2, 3, 4) have been reported. X-Ray determina-

tions revealed that [Li2(P2Ph2)(TMEDA)2] and [Li2(P4Ph4)(TMEDA)2] are triple

ions, while for n = 3 the ion pair [Li(TMEDA)2]+[Li(P3Ph3)(TMEDA)]� is

observed.61 The compound [Li(NH3)4]4[(P14NH3)N] has been prepared by the

reduction of white phosphorus with elemental lithium in liquid ammonia.62


The electronic effects of substituents on aggregation 4-methoxy- and 4-cyano-

substituted lithium aryloxides have been studied. Solution and solid state studies

indicated that the methoxy complexes are more highly aggregated than the cyano

derivatives.63 Treatment of 2,6-dibenzylphenol (HOdbp) or 20,200-dimethoxy-2,6-

dibenzylphenol (HOdbpOMe) with nBuLi or sodium bis(trimethylsilyl)amide af-

forded the dimeric alkali metal phenolates [{M(Odbp)L}2] (M = Li; L = Et2O,

L = DME, M = Na; L = Et2O, L = DME), [{Li(OdbpOMe)}2] and [{M(Odb-

pOMe)L}2] (M = Li; L = DME, M = Na; L = THF, L = DME.64 Two mixed

lithium/calcium phenolates have been characterised in the solid state. [CaLi6-

(m3-OPh)8(THF)6] was obtained from the reaction of CaI2 with LiOPh in THF

and features two hetero-cubane units fused via the calcium ion. Upon recrystallisa-

tion from DME, the aggregate [Ca2(DME)2(m-OPh)6{Li(DME)}2] was obtained.65

The alkali metal salts [TCALi4], [TCANa4], and [TCALK4] of fully deprotonated

H4TCA were isolated from reactions of the thiacalix[4]arene and nBuLi, NaH, or

KH.66 Several polynuclear aggregates have been obtained by reaction of [(m3,m3-EDBP)Li2]2[(m3-

nBu)Li(0.5Et2O)]2 with primary alcohols, some of which showed

great reactivity toward ring-opening polymerisation of L-lactide.67

3. Sodium and potassium

Heavier alkali metal reagents played a role in the isolation of several landmark main

group compounds in 2006. The first ‘‘dialuminyne’’ species Na2[Ar0AlAlAr0]

[Ar0QC6H3-2,6-(Dipp)2] and the ‘‘cyclotrialuminene’’ Na2[(AlAr00)3] [Ar00QC6H3-

2,6-(Mes)2) were synthesised by reduction of solutions of Ar0AlI2 and Ar00AlI2 with

excess sodium. In both compounds the sodium ions are coordinated to the flanking

aryl rings of the terphenyl ligands.68 Reaction of [tBu2MeSiNa] with SnCl2 in THF

afforded [(tBu2MeSi)2SnQSn(SiMetBu2)2], the first example of an acyclic distannene

with a SnQSn double bond that is stable both in the crystalline form and in

solution.69 The synthesis of [{K2(VO)2(OPr)6(PrOH)2}N] has been reported.70

Amido-tethered N-heterocyclic carbene (NHC) lanthanide complexes, [Ln(L)N002]

[L = tBuNCH2CH2{C(NCHCHNtBu)}; N00 = N(SiMe3)2; Ln = Y, Sm], when

treated with potassium naphthalenide, undergo regiospecific deprotonation at the

NHC backbone to generate the Ln–K heterobimetallic complexes [N002Ln(L)-

K(DME)]2 [Ln = Y, Sm; L = the dianion tBuNCH2CH2{C(NCCHNtBu)}].71

Treatment of [(Me3Si)(Me2(MeO)Si)CH(SiMe2CH2)] with two equivalents of MeK

gave [{(Me3Si)(Me2(MeO)Si)C(SiMe2CH2)}2K2]n. Similarly, treatment of [(Me3-

Si)2(Me2(MeO)Si)CH] gave [{(Me3Si)2(Me2(MeO)Si)C}K]N.18 Reaction of

[6-Me(2-Py)(Me3Si)2CH] with (nBuM) (M = Na, K) in the presence of PMDTA

and TMEDA resulted in the formation of [{6-Me(2-Py)}(Me3Si)2CNa(PMDTA)]



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and [{6-Me(2-Py)}(Me3Si)2CK]N.72 1,3- and 1,4-bis[tris(trimethylsilyl)silylethynyl]-

benzene and 1,3,5-tris[tris(trimethylsilyl)silylethynyl]benzene undergo di- or tri-

metallation with KOtBu to afford the respective oligosilyldi- and tri-anions.73

The X-ray crystal structures of several nitrogen heterocycles bonded to (18-crown-

6) potassium fragments with Z2-bonding interactions have been described.74 The

optimised syntheses of the alkali metal tris(pyrazol-1-yl)borates [M{Me2NBpz3}]

(M = Na, K) and [K[{PhBpz3}] have been described.75 Three alkali metal ion

complexes, [Na{N(SiHMes2)2}(OEt2)], [Li{N(SiHMes2)2}] and [K{N(SiHMes2)2}]

have been synthesised and discussed.76 [HN(SiMe2Ph)2 has been reported to react

with KH or NaH to produce dimeric compounds [KN(SiMe2Ph)2]2, and [Na{N(Si-

Me2Ph)2]2.77 Reactions of [M{CH(SiMe3)2}] (M = Na or K) with PhCN resulted in

several Na and K azaallyls and b-diketiminates.78 Reactions between a sodium

amide [Na{N(SiMe3)R}] (R = SiMe3, SiMe2Ph or tBu) and cyanoalkanes have been

investigated and the outcomes determined by X-ray diffraction.79 A new ligand

creating two sites reminiscent of b-diketiminates, has been reported. Upon depro-

tonation with KH the salts exist in oligomeric forms with potassium ions linking

multiple ligands.80

The reactivity of [NaMgBu3] and [Na2MgBu4] toward 2,4,6-trimethylacetophe-

none has resulted in the synthesis of a series of mixed sodium–magnesium enolate

complexes.81 The sodium-mediated zincation of polycyclic aromatic hydrocarbons

has been shown to be a viable route to mono- and dizincated naphthalenes.82 A

solvent-free polymeric variant of a previously reported hydride-containing inverse

crown, [Mg2Na2H2(C6H14N)4], has also been prepared.83 Metalation of N,N-

dimethylaniline with the heterometallic [(TMEDA)Na(tBu)(TMP)Zn(tBu)]2switched the orientation of the deprotonation to the meta site from the more normal

ortho. The carbanion generated by this regiospecific meta-proton abstraction was

stabilised through coordination to a bimetallic alkyl amido cation.84 Furan is

deprotonated at the a-position by [(TMEDA)Na(nBu)(m-TMP)Mg(TMP)].85 The

first sodium alkyl(TMP) aluminate reagent to be synthesised, [TMEDA �Na-

(m-TMP)(m-iBu)Al(iBu)2], reacted as an amido base towards phenylacetylene to

form [(TMEDA)2Na(m-CCPh)(m-iBu)Al(iBu)2]. In contrast, the TMEDA-stabilised

lithium (TMP) aluminate exhibited dual alkyl/amido basicity with N,N-diisopro-

pylbenzamide to form a heterotrianionic crystalline complex [{PhC(QO)-

N(iPr)2} �Li{2-[1-C(QO)N(iPr)2]C6H4}{Me2NCH2CH2N(Me)CH2}Al(iBu)2], which

also contains a deprotonated TMEDA ligand and a neutral benzamide molecule

ligated to lithium.86 Bis(toluene)chromium is regioselectively deprotonated at the

para-position by a mixed sodium–magnesium alkyl bis(amide) synergic base in a

reaction influenced by Na� � �p-arene contacts.87

Tetrasodium tetradecaphosphide Na4P14 has been obtained and the structures of

[Na4(DME)7.5P14] and [Na4(en)6P14] described.88 Crystal structures of [K(18-crown-

6)2P4(NH3)2], [(Rb(18-crown-6)2(P4)0.85(As4)0.15)(NH3)3], and [(K(18-crown-

6)2(As)4] have been described. All three compounds feature neutral molecules with

a tripledecker coordination of the cyclotetrapnictide anion between two alkali metal

cations.89 The alkali metal tetraphosphanediides [K2(PMDETA)2(P4Ph4)] and

[K2(PMDETA)(P4tBu4)]2 have been synthesised by reaction of PhPCl2 or tBuPCl2

with potassium.90 The scope of hypersilyl potassium, KHyp, as a silylation or

deprotonation agent for some rare-earth bis(trimethylsilyl)amides has been ex-

plored. Reaction with [Yb{N(SiMe3)2}2] afforded the addition product

[K][YbHyp{N(SiMe3)2}2], while silylmethyl deprotonation is observed with

[Ln{N(SiMe3)2}3] (Ln = Y, Yb).91 The novel hypersilylphosphanides [HypPHK]



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and [Hyp(Me3Si)PK] have been prepared by reactions of the parent phosphines withtBuOK.92 Treatment of the phosphine-borane adduct [(Me3Si)2{Me2P(BH3)}CH]

with either MeNa or MeK in diethyl ether yielded the alkali metal salts [(Me3Si)2-

{Me2P(BH3)}CML]N [ML=Na(THF)2 � 1/2PhMe; K], the first heavier alkali metal

complexes of a phosphine–borane-stabilized carbanion.93 The polyphosphide anions

in ethylenediamine/2,2,2-crypt and ethylenediamine/18-crown-6 have been isolated

as [K(2,2,2-crypt)]3(HP7)2 � en and [K(18-crown-6)]2(HP7).94

The benzophenone dianion [Ph2CO]2�, has been crystallised with sodium cations

to form the polymeric chain compounds [Na2(Ph2CO)(tetraglyme)]N and [Na2(Ph2-

CO)(THF)2]N.95 The potassium salt of a p-t-butylcalix[6]arene p-bromophenylala-

nine derivative forms a self-assembled octameric cage in the solid state.96 The

compounds [M2Co2(m3-OtBu)2(m

2-OtBu)4(THF)n] (M = Na, n = 2; M = K, n =

0; M = Rb, n = 1) have been synthesised.97 Metathesis of [Ln(thd)3] (Ln = Pr, Nd,

Eu, Tb) with one or two equivalents of group 1 salts of the sulfur-bridged

binaphtholate dianion [1,10-S(2-OC10H4tBu2-3,6)2]

2�, [M2L], (M = K, Li) gave

luminescent complexes ML[LnL(thd)2].98 The thiodiphosphate, [Na(12-crown-

4)2]2[P2S6] CH3CN, has been synthesised by the reaction of Na2[P2S6] with

12-crown-4 in dry acetonitrile.99

4. Rubidium and caesium

New polyiodides of caesium containing double and triple decker cations, [Cs(benzo-

18-crown-6)2]Ix and [Cs-2(benzo-18-crown-6)3]Ix (x = 3, 5) have been charac-

terised.100 Treatment of [Cs{(CF3)3BNH2}] with the aminating agent H2NOSO3H

in aqueous solution allowed the isolation of pure [Cs{(CF3)3BH}].101 Crystallisation

of C-methyl pyrogallarene with potassium, rubidium and caesium bromides or

chlorides resulted in a hydrogen bonded molecular cage in which the alkali metal

cations are Z6-coordinated to the aromatic rings via strong cation–p interactions.102

Metathesis reactions between [(Me3Si)2{Me2P(BH3)}CLi] and either rubidium or

caesium 2-ethylhexoxide gave the compounds [[(Me3Si)2{Me2P(BH3)}C]ML]n[ML = Rb, n = N; Cs(PMDTA), n = 2].93

5. Beryllium

Multigram amounts of [BeBr2(SMe2)2] were synthesised by heating Be powder in a

Br2 atmosphere and condensing Me2S on the formed BeBr2. The compound is very

soluble in Me2S and CH2Cl2 and is a versatile starting material for ether-free

homogenous reactions.103 Beryllium chloride reacts in dichloromethane suspension

in the presence of an equimolar amount of 12-crown-4 with SbCl5 to give [BeCl(12-

crown-4)]+[SbCl4]�.104 [(Ph4P)2(Be2F6)] reacts with excess trimethylsilylazide in

acetonitrile, accompanied by a hydrolytic side-reaction, to give the azido beryllate

[(Ph4P)2{Be(m-OSiMe3)(N3)2}] as colourless, non-explosive crystals.105 The reaction

of base-free Ph2Be with 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (iPr-car-

bene) in toluene gave the carbene adduct Ph2Be(iPr-carbene), the first carbene

complex of a diorganoberyllium.106 The low-dimensional beryllium phosphates,

[C5H14N2]2[Be3(HPO4)5] �H2O and [C6H18N2]0.5[Be2(PO4)(HPO4)OH] � 0.5 H2O,

have been synthesised under mild hydrothermal/solvothermal conditions.107



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6. Magnesium

Cocondensation reactions of heterocyclic aromatic compounds with calcium and

magnesium atoms at 77 K resulted in C–H bond activations and led to the

corresponding aryl metal compounds for Ca but not Mg.108 The magnesium- and

calcium-gallium heterocycle complexes [Mg{Ga[(ArNCH)2]}2(THF)3], 1, and [Ca-

{Ga[(ArNCR)2]}2(THF)4], (R = H or Me, Ar = Dipp), prepared by the reduction

of [I2Ga{(ArNCR)2}] with the group 2 metals, exhibit the first structurally authen-

ticated Ga–Mg and Ga–Ca bonds in molecular species.109 Treatment of a series of

a,o-boryl(bromo)alkanes, R2B(CH2)nBr (n= 3, 4, 5, 6) with Mg turnings resulted in

the respective Grignards. All alkanes with n = 4 to 6 underwent an unprecedented

boron-centered cyclisation reaction with formation of borate-cyclopentanes,

-hexanes (e.g. 2), and-heptanes, respectively.110

The first reports of Grignard reagents generated in the ionic liquid nbutylpyr-

idinium tetrafluoroborate have appeared showing different reactivity from classical

Grignard reagents in organic solvents.111 The synthesis and structure of

[{MgCl(THF)2}3(m3-C3H5)2]2[Mg(C3H5)4] has been reported.112 The bis(phosphini-

mino)methanide [CH(Ph2PNC6H2-2,4,6-Me3)2]� has been employed in the synthesis

of a variety of heteroleptic complexes of Mg including the dimer [{CH(Ph2PNC6H2-

2,4,6-Me3)2}MgCl]2 and the monomer [{CH(Ph2PNC6H2-2,4,6-Me3)2}-

MgCl(THF)].113 The possibility of selective use of each epimeric component of the

classic chiral Grignard reagent (1R,2S,5R)-menthylmagnesium chloride in reactions

with electrophiles using thermodynamic/kinetic control has been proposed.114 The

synthesis of functionalised benzylic magnesium reagents through a sulfur–magne-

sium exchange had been described.115 A halogen/magnesium-exchange reaction has

been employed in the preparation of a range of five- and six-membered functiona-

lised heteroaryl magnesium compounds. Their reactions with various electrophiles

provided entry to a range of polyfunctional heterocycles such as thiophene, furan

and pyrrole derivatives.116 Grignard reagents have been found to add to a,b-unsaturated thioesters in a 1,4-fashion and the resulting magnesium enolates trapped

with aromatic or aliphatic aldehydes. The process provided a range of products

bearing three contiguous stereocentres with control of relative and absolute stereo-

chemistry.117 It has been reported that efficient alkylation of ketones and aldimines

with Grignard reagents may be catalysed by zinc(II) chloride.118

The synthesis of bis(polysilanyl)magnesium and polysilanylmagnesium bromide

compounds has been accomplished by metathesis of the potassium polysilanyls with

magnesium bromide. The use of PhMgBr and MeMgBr instead of magnesium

bromide led to the formation of mixed alkyl/polysilanylmagnesium compounds.119

6.1 Group 15 donors

[Mg(NH3)2(N3)2] has been synthesised from Mg3N2 and NH4N3 in liquid ammonia

as a colourless powder which can detonate above 180 1C.120 The magnesium



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analogues of some paramagnetic Mn2+ complexes have been prepared by the

reaction of the ligand precursors [P(CH2NHPh)3], [P{CH2NH-3,5-(CF3)2C6H3}3],

and [P(CH2NH-3,5-Me2C6H3)3] with (nBu2Mg) and the solid-state structures deter-

mined.121 Amides of the type R2NMgCl �LiCl have been found to act as highly

efficient bases for the regioselective generation of functionalised aryl and heteroaryl

magnesium compounds.122 The heterobimetallic compound [(Me3Si)2NMg{m-N-

(SiMe3)2}2CaN(SiMe3)2] was prepared via equilibration of [Mg{N(SiMe3)2}2] and

[Ca{N(SiMe3)2}2]2. Addition of pyridine resulted in asymmetric cleavage of the

mixed-metal ring structure, to form a charge-separated ate species

[(Me3Si)2NCa.(py)n]+[Mg{N(SiMe3)2}3]

�.123 Compounds of composition

[RMgN(CH2CH2OMe)2] and [RMg(N15C5)] have been prepared.124 Reaction of

the imino sulfinamidine [PhS(NHtBu)QNC(Me)QN(Dipp)], LH, MgI2, and

[KN(SiMe3)2] resulted in the formation of the magnesium complex, [LMg{N-

(SiMe3)2}(L2Mg)].125 Treatment of dimethylmagnesium with the a-diimine ligands

[DippNQC(R)C(R)QNDipp] (R = naphth-1,8-diyl, H, CH3) provided the methyl-

bridged complexes, [(a-diimine)Mg+(m-CH3)]2, via single electron transfer to the

coordinated diimine and elimination of a methyl radical. The biradical species have

been characterised by EPR.126 The first magnesium bam complexes have been

synthesised via reactions between dilithiobam and Grignard reagents or MgCl2.

Several new classes of bam complexes have been structurally characterised including

the heterobimetallic spirocycle [{(Et2O)-m-Li[PhB(m-(NtBu)2]}2Mg].127 [Mg-

{N(SiMe3)2}2], reacts with substoichiometric amounts of propiophenone to form a

74:26 mixture of the enolates (E)- and (Z)-[{(Me3Si)2N}2Mg2(m-{N-

(SiMe3)2}){m-OC(Ph)QCHCH3}].128 Compounds with the Mg–O–Al structural

motif have been prepared as models for the fixation of organometallics on a MgO

surface.129 The synthesis, structure, gas sorption and guest-exchange properties of

the lightweight, porous metal-organic framework a-[Mg3(O2CH)6] has been pub-

lished. Thermogravimetric analyses show guest loss from 120–190 1C and decom-

position at 417 1C, while gas sorption studies using both N2 and H2 indicated that

the framework displays permanent porosity.130 Four novel alkaline earth metal

tetranuclear aryloxide/pyrazolate hydroxides of the general formula M4(ligand)6-

(OH)2(donor)n, [M = Mg, Ca, Sr], have been prepared by either adding stoichio-

metric quantities of water to preformed alkaline earth metal aryloxides or via a direct

combination of the metal, ligand (alcohol, pyrazole), and donor with stoichiometric

amounts of water. The compounds are considered as potential intermediates in the

sol-gel process.131

7. Calcium, strontium and barium

The first hydrosilylation catalysts based on early main-group metals (Ca, Sr, and K)

have been reported as very effective for the conversion of conjugated double bonds.

The catalytic reactions are initiated in all cases by the formation of a highly reactive

metal hydride, which either adds to an alkene or to the silane.132 Reaction of

[CH{(Me)CN(Dipp)2}Ca{N(SiMe3)2}(THF)] with an excess of phenylsilane has

provided the first example of a well defined and hydrocarbon-soluble calcium

hydride, 3. The hydride complex displayed remarkable thermal stability.133 The

reaction of activated calcium with aryl halides gave compounds of the type RCaX

([MesCaI(THF)4], [(p-tolyl)CaI(THF)4], [PhCaI(THF)4], and [PhCaBr(THF)4]) in

fair to good yields. All of these ‘‘heavy Grignard reagents’’ contain a calcium atom

in a slightly distorted octahedral environment and must be handled at low



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temperatures in order to avoid ether cleavage reactions.134,135 A series of heteroleptic

calcium Z5-C5R5 cyclopentadienides have been synthesised by protonolysis of

[HC{C(Me)N(Dipp)}2Ca{N(SiMe3)2}(THF)] with tetramethylcyclopentadiene,

fluorene, indene or cyclopentadiene.136 Homoleptic [{CH(Ph2PNC6H2-2,4,6-

Me3)2}2M] (M = Ca and Ba) and heteroleptic [{CH(Ph2PNC6H2-2,4,6-Me3)2}M-

{N(SiMe3)2}(THF)] (M = Ca, Sr) bis(phosphinimino)methanide complexes have

been readily provided by a ‘‘one-pot’’ procedure utilising the appropriate diiodide

and variation of [CH2(Ph2PQNC6H2-2,4,6-Me3)2] and [KN(SiMe3)2] stoichiome-

try.113 Attempted 2-fold deprotonation of the bis(phosphinimino)methane ligand,

[H2C(Ph2PQNSiMe3)2] with a calcium amide also led only to mono-deprotonation.

Reaction of with a dibenzylcalcium complex, however, gave 2-fold deprotonation

and formation of a dimeric ‘carbenoid’ Ca complex, 4.137 The structures of several

adducts of bis(fluorenyl)barium have been described.138

The pure rotational spectrum of BaNH in its ground electronic state has been

recorded from molecules produced by the reaction of NH3 and barium vapour in the

presence of a dc discharge. Molecular orbital analyses of the BaNH wave function

showed that Ba–N p bonds formed by the formally filled N 2p orbitals of the imido

group to the empty Ba 5d orbitals, along with the ease of oxidation of the Ba atom,

favour formation of the metal-imido over that of the metal-amido species.139 The

ternary imide of [MgCa(NH)2] has been successfully synthesised by the mechan-

ochemical reaction of [Mg(NH2)2] and CaH2. It was found that ca. four H atoms

were desorbed per [Mg(NH2)2CaH2] after ball milling.140 The first homoleptic

alkaline earth (Tf2N) complexes [{mppyr}2{Ca(Tf2N)4}], [{mppyr}{Sr(Tf2N)4}]

and [{mppyr}{Ba(Tf2N)3}] were crystallised from a solution of the alkaline earth

bis(trifluoromethanesulfonyl)imide and the ionic liquid [mppyr][Tf2N].141 Three

new complexes of 1,10-phenanthroline (phen), [Ca(phen)2(H2O)2(NO3)](NO3),

[Sr(phen)2(H2O)2(NO3)](NO3) and [Ca(phen)2(H2O)2(NO3)][BF4] have been synthe-

sised and characterised by UV, FTIR and Raman spectroscopies. Reaction of

[{MeAl(2-py)3}Li(THF)] and CaI2 gave the trimetallic complex [{MeAl-

(2-py)3}2Ca].142

Complexes of the heavier alkaline earth metals containing bulky b-diketiminate

and iodide ligand sets have been described. Treatment of the potassium b-diketimi-

nate with equimolar amounts of MI2 (M = Ca, Sr, Ba) afforded a variety of

hapticities from Z2 to Z5-, which were dependent upon the identity of the metal and

the molecularity of the complex.143 A tris-pyrazolylborate ligand bearing ether

appendages was shown to be hemilabile by NMR studies and structural character-

ization of its Z3, Z5, Z6, and m-binding modes in coordination with Li+, Na+, K+,

Tl+, and Ca2+ ions.144 A new series of dinuclear alkaline-earth pyrazolates,

[{M(3,5-tBu2pz)2}n] (M = Ca, n = 3; M = Sr, n = 4; M = Ba, n = 6) have been

obtained from the donor-free complexes by treatment with THF.145 A bis(diphos-

phanylamido) complex of strontium [{(Ph2P)2N}2Sr(THF)3] has been prepared by



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reaction of [K(THF)n][N(PPh2)2] (n = 1.25, 1.5) and SrI2. In contrast, reaction of

[K(THF)n][N(PPh2)2] with BaI2 gives the coordination polymer [{(Ph2P)2N}2-

Ba(THF){(Ph2P)2N}K] because of the increased radius of the Ba2+ cation.146

Hydrolysis of a calcium-amide provided a (b-diketiminate)calcium-hydroxide

complex, 5, that is remarkably stable against ligand exchange and formation of

[Ca(OH)2]. The structure of this dimeric complex has OH- units that symmetrically

bridge the Ca2+ ions. This hydroxide reacted rapidly with CO2 to produce a gel

allowing sol-gel coating with CaCO3 from an organic solvent.147 Reactions of the

bulky amino-bis(phenol) ligand [Me2NCH2CH2N{CH2-3,5-tBu2C6H2OH}2] with

[Mg{N(SiMe3)2}2] and [Ca{N(SiMe3)2}2(THF)2] yielded the LM complexes in good

yields. The calcium complex was an active initiator for the ring-opening polymer-

isation of e-caprolactone (up to 97% conversion of 200 equivalents in 2 hours) and

yielded polymers with narrow molecular weight distributions.148

Heating a solution of [Cp2Ca{H10}] in DMSO-d6 for 1 hour at 150 1C afforded

Cp2Ca{d10} (97% D) cleanly in 95% isolated yield. For the ring-substituted bis(1-

cyclopentenyl)calcocene, H/D exchange occurred at the 2,5-positions of the

1-cyclopentenyl substituents as well as at the cyclopentadienyl rings.149 Treatment

of calcium or strontium with 2 equivalents of N,N0-bis(o-methylphenyl)formamidine

(o-tolFormH), N,N0-bis(2,6-dimethylphenyl)formamidine (XylFormH) or N,N0-

bis(o-phenylphenyl)formamidine (o-PhPhFormH) in the presence of one equivalent

of [Hg(C6F5)2] afforded the bis(formamidinate) complexes [Ca(o-Tol-

Form)2(THF)2], [Ca(XylForm)2(THF)2], [Ca(o-PhPhForm)2(THF)2], and [Sr(o-

PhPhForm)2(THF)3].150 Reactions of Ca, Sr and Ba chlorides with 2-hydroxy-1-

naphthaldehyde and 2-hydroxybenzophenone or 5-halosalicylaldehyde have yielded

mixed ligand complexes of the type [MLL0(H2O)2].151

Ligand/reagent abbreviations

bam boraamidinate

Cy cyclohexyl

Dippbian 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene

Dipp 2,6-diisopropylphenyl

EDBPH2 2,20-ethylidenebis(4,6-di-tert-butylphenol)

HMPA hexamethylphosphoramide

HN15C5 1,4,7,10-tetraoxa-13-azacyclopentadecane)

H4TCA p-tbutyltetrathiacalix[4]arene

Hyp tris(trimethysilyl)silyliPr-carbene isopropyl-4,5-dimethylimidazol-2-ylidene

LDA lithium diisoproylamide

Mes 2,4,6-trimethylphenyl

mppyr 1,1-N-methyl-N-propylpyrrolidinium

py pyridyl

Pz pyrazol-1-yl

t-DACH trans-1,2-diaminocyclohexane

Tf2N bis(trifluoromethanesulfonyl)imide

thd 2,2,6,6-tetramethylheptanedionate

TMCDA trans-N,N,N0,N0-tetramethylcyclohexanediamine

TMEDA N,N,N0,N0-tetramethylethylenediamine



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TMP 2,2,6,6-tetramethylpiperidide

Trip 2,4,6-triisopropylphenyl

Tript triptycenyl

Tsi tris(trimethysilyl)methyl

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alkali and alkaline-earth metals

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